Link failure includes control channel failure and TE link failure.
Handling Impassable Control Channels
Control channels are classified into control channels inside and outside fibers. The control channels inside fibers use D4-D12 bytes to transmit the check information. The control channels outside fibers are seldom used.
Handling Impassable TE Links
TE links can be checked only when control channels between adjacent nodes are available in an ASON network.